1. Field of the Invention:
The present invention relates to flywheels. More particularly this invention relates to flywheels that can change vibrational behaviors, thereby suppressing resonance.
2. Description of the Related Art:
Flywheels which comprise means defining two inertia moments (driving and driven side flywheels), a spring mechanism for connecting the two inertia moment defining means and a friction mechanism are well-known, as demonstrated by U.S. Pat. No. 4,468,207, U.S. Pat. No. 4,274,524, U.S. Pat. No. 4,351,168, U.S. Pat. No. 2,042,570U.S. Pat. No. 4,445,876, U.S. Pat. No. 2,729,079, U.S. Pat. No. 2,437,537, DE-A-2,926,012, Automotive Enginnering, vol. 93, page 85, etcetera.
The prior art flywheels have a single kind of vibrational characteristic produced by a single kind of spring mechanism, even though the single kind of spring mechanism may comprise a plurality of coil springs provided in series or in parallel with each other. The single vibrational characteristic causes the flywheel to have a single first mode resonance speed through all engine speeds. The resonance speed is usually set lower than the idling speed of the engine. As a result, when the engine speed passes through the resonance speed during a start-up or stop operation, torsional vibrations of the flywheel are amplified. To suppress the amplification in the torsional vibrations to a low level, a continuously sliding friction mechanism (a hysteresis mechanism) which slides through the entire range of the engine speeds is disposed between the two inertia moment defining means
However, there are the following two deficiencies in the prior art flywheels. One deficiency is that a considerably large resonance remains at the resonance speed even if the friction mechanism is provided, because the characteristic of the flywheel is determined mainly by the spring mechanism and less by the friction mechanism The other deficiency is that the friction mechanism deteriorates the acceleration transmitting rate (which corresponds to a damping characteristic of the flywheel) in the standard range of engine speeds above the idling speed, because the continuously operates over the entire range of engine speeds and because temporary sticking often occurs in the friction mechanism.